Long-lived impulse transformer



June 21, 1960 F. FRUENGEL 2,942,214

LONG-LIVED IMPULSE TRANSFORMER Filed March 7, 1957 2 Sheets-Sheet 1 &

TTOPA/E) June 21, 1960 F. FRUENGEL LONG-LIVED IMPULSE TRANSFORMER 2 Sheets-Sheet 2 Filed March 7, 1957 ATTORNEY States Unite LONG-LIVED IlVIPULSE TRANSFORMER Frank Fruengel, Wittenbergenerwe 79, Hamburg- Rissen, Germany This invention relates to transformers for impulse service such as used in impulse welding machines and impulse magnetizers for permanent magnets where instantaneously heavy current impulses have to be transformed. Transformers of prior design for this type of service have relatively short life and it is a primary object of this invention to provide an improved impulse transformer that is of rugged construction and long lived. As practical service has shown, the transformer provided by this invention is good for a useful life of transforming more than 50 millions of actual work-ing impulses.

The new and unique transformer construction as provided by this invention is characterized in that the primary winding comprises a plurality of winding sections each forming a coil of a plurality of winding turns embedded in a disc-type hard plastic body which is suspended in a damping medium, preferably a silicone fluid, confined in a shell forming a portion of a one-turn secondary winding. By virtue of the damping medium between primary and secondary windings, no destructive mechanical forces created by heavy currents can become active on these windings whereby the life of the winding structure is materially increased. The damping medium is preferably of high viscosity and lends the whole structure sufficient mechanical stability.

For a better understanding of the invention, a detailed description with reference to the accompanying drawing will now be given. In the drawing,

Fig. 1 is a longitudinal section of a disc-type body of hard plastic in which a coil of primary windings is embedded,

Fig. la is a section on the line 1a-1a of Fig. 1,

Fig. 2 is a longitudinal section of a transformer according to the present invention,

Fig. 2a is a section on the line 2a-2a of Fig. '2,

Fig. 3 is a plan view of a transformer end plate, and

Fig. -4 is a diagram of a welding circuit in which the impulse transformer of the present invention is employed.

Referring to the drawing and more particularly to Figs. 1 and la, there is shown a disc 1 of hard plastic material in which are embedded the window turns 2 of a coil having about 20 turns of wire. Beginning and ending or the terminals 4 of the coil are brought out through a cylindrical projection 3 at the outer cylindrical surface of disc 1. Disc 1 with its coil forms a section of the primary winding of the transformer. A plurality of such sections 1, 2 are connected by wires 5 which join terminals 4 of adjacent coils as shown in Fig. 2. Each disc 1 is enclosed or completely surrounded by a metal shell or casing 6 forming a portion of the one-turn secondary winding of the transformer. Sufiicient clearance is provided between the outer surface of disc 1 and the inner wall of shell 6 to provide space for a filling of a damping me-, dium 7, preferably a fluid having high viscosity such as a silicone. In this manner disc 1 with embedded winding turns 2 is actually suspended in such fluid. As best shown in Fig. 2a the outer wall ofshell 6 is flared out at one point to form a. tubular projection 8 which accommodates atent 2,942,214 Patented June 21, 1960 the cylindrical portion 3 of disc 1 with terminal leads 4.

A sealing ring 9, preferably of insulating material, is interposed between shells 6 cooling units 11 and two such units are indicated in Fig. 2. They consist of a coil of tubing cast in a disc 12 of heat-conducting material such as lead. Discs 12 have substantially similar shape as shells 6. Inlet and outlet 13 of this tubing are brought out for connecting to a source of cooling medium. A plurality of shells 6, forming each a portion of the secondary winding and enclosing primary winding sections 1, 2, are arranged on a tube of insulating material 14. As best shown in Fig. 2a, each shell 6, having tubular projection 8 at one point, is separated by a radial dividing slot 16 extending through its entire section. This slot is shown in Fig. 2a at the bottom and is necessary to obtain an open-circuited one-turn winding portion. A spacer 17 of insulating material is inserted in slot 16 to insulate the opposite terminals of the secondary winding. The terminals for connecting the leads (not shown) are formed by radially outwardly extending ears 18 of the outer wall of shell 6. Reenforcement angles 15 are secured by wending or otherwise to the ears, and cars 18, as well as angles 15 are provided with holes for a bolt 19 preferably of nonmagnetic material. The bolt is electrically insulated from the terminal portions 18 by insulating bushing 21, and is provided to take up the considerable mechanical forces acting between the opposite terminals when heavy impulse currents are passing through them.

The iron core 22 of the transformer is preferably of the open magnetic circuit type i.e. has a length substantially equal to that of said secondary formed by the stack of shells 6, and comprises as shown a laminated bar upon which insulating tubing 14 and the winding sections are arranged. The winding sections are secured in place by end plates 25 which in turn are fastened by a preferably nonmagnetic bolt 23 extending in an opening 23a provided therefor through the whole length of core 22. Bolt 23 is preferably insulated from the core by a sleeve of insulating material 24. A plan view of plate 25 is shown in Fig. 3 and it will be noted that a radial slot 27 is provided therein to prevent this plate from forming a short-circuited secondary in which an undesirable current would be induced.

A wiring diagram in which a transformer of the present design is employed is depicted in Fig. 4. A highvoltage source is shown at 28 and is connected for charging condenser 30 by way of suitable switching means 29. The condenser is connected to discharge into the primary 32 of the transformer by way of switching means 31. The secondary of the transformer is connected to the work load '34, for instance, through the electrodes of a welding machine.

The damping medium introduced between the primary and secondary windings of each winding section, which, as already stated, is preferably a silicone fluid of high viscosity, in some cases can be a powdered substance having good antifriction properties, such as talcum or the like. A cooling system as illustrated in Fig. 2 is necessary for heavy working loads only and in transformers for normal operating loads, cooling by an externally applied blast of air is mostly sufficient. In such designs it is better to omit the cooling units 11 and place all shells 6 adjacently to one another in order to obtain close coupling between primary and secondary windings throughout.

In impulse operation, for which the transformer of the present invention is designed, every current impulse causes instantaneous magnetization of the iron core. Since the instant of magnetization is too short to produce a magnetic flux throughout a magnetic circuit, the open core type transformer, in which a laminated bar is employed,

- serves well. In such a transformer, the mechanical forces as possible, it is advisable to use a poor grade of mag-.

netic material with high hysteresis losses for the core. With an open-circuited secondary or a highly inductive load, high hysteresis in the core effects considerable damping of circuit oscillation without causing noticeable diminution in the first peak of the discharge which is essential for the process in the work load. Moreover, the damping effect of a poor grade of core material reduces also the magnitude and duration of the mechanical forces set up by heavy currents between coils and core and preserves mechanical strength toward longer transformer life.

The single bolt 23 through the center of core 22 and through end plates 25 is shown in Fig. 2 for illustration of construction only and it will be understood that other methods of assembling can be employed, for instance, with several bolts and these at the outside of the periphery of the winding sections.

While I have described what I at present consider the preferred embodiment of my invention, it will be apparent that various changes and modifications may be made without departing from the true spirit and scope of my invention, and it is therefore my aim to cover all such changes and modifications by the appended claims as fully as rightfully possible.

What I claim is:

. 1. An impulse transformer having a core of magnetic material, a plurality of disclike hollow metallic shells provided each with a radial dividing slot being stacked on said core in electrical contact with one another and with said dividing slots in axial alignment to form in combination a one-turn secondary of said transformer, a primary coil constituted by a plurality of coil units, each unit comprising a plurality of winding turns and a disclike body of insulating material surrounding said turns, each of said units being inserted in the hollow of one of said shells in spaced relation to the inner Wall thereof to provide a space between said wall and said coil units, a

sulating material surrounding said turns, and one secondary winding turn, said secondary winding turn being in the form of a metal shell substantially completely surrounding said primary coil unit in spaced relation, a filling of damping medium introduced in the space between said primary coil unit and said secondary winding turn, each secondary turn being in electrical contact with the secondary turn of the adjacent winding section whereby all secondary turns are arranged in parallel to form a one-turn secondary of the transformer, said primary winding turns of said coil units of all sections being inter-connected to form the primary of the transformer.

6. An impulse transformer having an iron core, a plurality of winding sections arranged as a stack on said core, the length of said core being substantially equal to the overall length of said stack, each'winding section comprising a disc of plastic material, a plurality of primary winding turns embedded in said disc, a metallic shell substantially completely enclosing said disc with sufficient clearance between the inner wall of said shell and the outer surface of said disc to provide a space all around said disc, at filling of a fluid of high viscosity introduced to fill said space, said shell having a radial dividing slot completely separating the annular continuity of said shell to form a portion of a one-turn secondary winding, means for connecting said primary winding turns said various winding sections to form the primary of said transformer, and means for inter-connecting in parallel said secondary winding portions to form a oneturn secondary of said transformer.

7. An impulse transformer having an iron core in the form of a bar, a plurality of winding sections arranged on said core, an opening through said core substantially parallel to the axis thereof, a bolt traversing said opening, an end plate at each end of said core secured by said bolt, said end plates radially extending to secure said winding sections in position on said core, each winding section comprising a disc of plastic material, a plurality of primary winding turns embedded in said disc, a metallic shell substantially completely surrounding said disc with suificient clearance between the inner wall of said shell and the outer surface of said disc to provide a space all around said disc, a filling of fluid of high viscosity introduced to fill said space, said shell having a radial dividing slot completely separating the annular continuity of said shell to form a portion of a one-turn secondary winding, means for inter-connecting said primary winding turns of said various winding sections to form the primary of said transformer, and means for filling of damping medium in all spaces so formed, and

connections for inter-connecting the winding turns of the individual coil units to form the primary of said transformer.

'2. An impulse transformer as in claim 1 wherein said damping medium is a silicone fluid of high viscosity.

'3. An impulse transformer as in claim 1 wherein said connecting in parallel said secondary winding portions to form a one-turn secondary of said transformer.

' 8. A winding section for an impulse transformer comprising a disc of hardened plastic material, a plurality of primary winding turns embedded in said disc and provided with leads, said disc having a portion projecting at one point of its periphery, said leads extending through said portion, a shell of metallic material surrounding said disc in spaced relation to form a space between the inner wall of said shell and the surface of said disc, a damping medium completely filling said space, said shell having a flared out tubular projection at one point of its periphery into which said projecting portion of said disc extends to form an outlet for said primary leads, said shell having further a radial dividing slot separating its annular continuity to form an open one-turn secondary winding.

9. A winding section as in claim 8 wherein sealing means are inserted between the tubular projection of said shell and the projecting portion of said disc to confine said damping mediumin its space.

10. An impulse transformer having a magnetic core, a plurality of winding sections arranged on said core, each winding section comprising a primary coil unit comprising a plurality of primary winding turns an insulating material sun-rounding said windings, one secondary winding turn in the form of a metal shell substantially-completely surrounding said coil unit in spaced relation, a filling of damping medium introduced in the space between said primary coil unit and said secondary winding turn, said shell having a radial dividing slot separating the continuity of said shell to form a portion of a one-turn secondary winding, means for inter-connecting said primary winding turns of all sections to form the primary of the transformer, means for connecting in parallel said secondary winding portions of all sections to form a one-turn secondary of the transformer, at least one cooling unit interposed between adjacent winding sections on said core, each cooling unit comprising a disc of heat-conducting material, and a coil of tubing embedded in said disc, said coil having inlet and outlet means adapted for connection to a source of cooling medium.

11. A winding section for an impulse transformer comprising a primary coil unit comprising a plurality of primary winding portions, insulating material surrounding said turns, and leads extending from said coil, a shell of current conducting material substantially completely surrounding said primary coil unit in spaced relation to provide a space all around said coil unit, a filling of damping medium introduced in said space, means for bringing out said primary leads through said shell, a radial dividing slot in said shell to interrupt the annular current-conductive continuity thereof for forming an open-circuited secondary winding turn, an ear projecting radially outwardly at each side of said slot to form a pair of terminals of said turn, an insulating spacer in said slot, reenforcement means secured to each ear, each ear and reenforcement provided with a hole, a nonmagnetic bolt passing through said holes in both ears to tie said ears for resisting the mechanical forces set up between the opposite terminals under heavy current load, and an insulating bushing inserted between said bolt and both holes to maintain electrical insulation between said terminals.

References Cited in the file of this patent UNITED STATES PATENTS 2,181,899 Kennedy Dec. 5, 1939 2,361,249 Venable Oct. 24, 1944 2,599,182 Kerns June 3, 1952 2,799,760 Fruengel July 16, 1957 

